Studies of food stickiness in relation to oral processing

It is generally accepted that a food perceived as sticky would adhere easily to oral surfaces (e.g. teeth and soft tissues) and lead to many irregular movements of the jaw and the tongue. However, there are two major issues with this assumption. Firstly, there has been no supporting experimental evidence. Secondly, the stickiness measurements in the research lab are often conducted under conditions very dissimilar to those in the mouth and, therefore, their correlations to oral experience are somewhat questionable. This project investigated food stickiness and its effects on oral experience using three approaches: instrumental characterization, sensory assessment, and oral physiological analysis. Six semi-solid confectionery foods, standardized in size and shape, were used for investigation. Their stickiness was characterized quantitatively using penetration tests performed in a Texture Analyser and evaluated sensorially through assessment by a taste panel of 14 young subjects. Oral response to food stickiness was characterised using surface Electromyography (sEMG) technique to record the activities of major oral/facial muscles. Products were well discriminated not only according to their stickiness but also their hardness. Instrumental characterization of food stickiness was carried out with two different probes: a flat 5mm stainless steel probe and a natural tooth probe, and measured dry and wet to mimic oral conditions. It was found that food products can be categorised into two groups: those in which stickiness increased and those in which the stickiness decreased after surface wetting. The measured wet stickiness exhibited very good correlations with sensory stickiness. Measurements from the sEMG of 10 subjects showed that the activities of oral muscles during mouth closing (masseters and temporalis), mouth opening (digastric muscle), and tongue movements respond directly to food stickiness. Increases in muscle work per chewing sequence W (µV-s) for both opening and clossing muscles were closely associated to the perception of food stickiness rather than with food hardness. Association of muscle activity, of closing muscles, to stickiness sensation is believed to arise from the increased difficulty and uncomfortable sensation of applying shearing action between teeth when the sticky food tends to hold them together.